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Executive summary

This report summarises findings of the project ‘More profitable crops on highly calcareous soils by improving early vigour and overcoming soil constraints’ (4.2.003), from four years of activities where the first three years were initially contracted and then extended for a fourth year.

Highly calcareous soils are common in some areas of south-eastern Australia and challenge crop production with a range of constraints. The challenges limit the effectiveness of improved agronomic practices developed elsewhere. This collaborative project, which started in 2020, aimed to identify and overcome calcareous soil constraints in order to lift crop production on these difficult soils. Replicated field trials were conducted on the upper Eyre Peninsula (EP) and in the South East (SE) of South Australia (SA) from 2020 to 2023 to investigate impacts of subsoil and topsoil amelioration strategies.

Findings from the work:

  • Short-term topsoil strategies resulted in better gains in crop biomass and yield when compared to longer-term subsoil strategies.
  • A carbon-coated mineral (bespoke biochar) applied in the topsoil improved crop vigour, biomass and grain yield as well as provided benefits to the following crop.
  • Increasing seeding rates and nutrition at sowing was effective at achieving high plant densities, crop biomass and grain yield.
  • High soil strength is an issue in calcareous soils, however, positive responses to deep ripping are less likely and usually limited by the hostile subsoil.
  • On very highly calcareous soils, improving the fertility of subsoils has the potential to improve grain yield, but responses only started showing in the third crop after application compared to the control.
  • Correcting severe yellowing in broad beans with multiple applications of iron chelate (EDDHA) resulted in more vigorous growth during winter and large grain yield increases on a highly calcareous soil in the SE region of SA.

Our findings may have direct applicability to other similar regions, despite considerable differences in farming systems and agroclimatic conditions. Addressing multiple constraints in calcareous soils using integrated solutions will ensure an increase in crop productivity and subsequently profitable and sustainable farming systems.

Objectives

The main aim of this research initiative was to identify and overcome the impacts of topsoil and subsoil conditions of highly calcareous soils on crop production in the SE and upper EP of SA. A holistic approach to addressing these constraints to crop productivity and profitability was implemented to better understand:

  • The benefits of organic matter and extra nutrient inputs on crop health and growth.
  • The impacts of a range of amendments on subsoil properties typical of Calcarosols.
  • The contribution of novel approaches (carbon coated minerals [CCM]) to phosphorus (P) supply, crop vigour and root health.
  • Current problems with crop emergence and fertiliser toxicity under marginal moisture conditions.
  • The impact of high soil strength and the contribution of a physical intervention to ameliorate compaction.
  • The role of manganese (Mn) and/or iron (Fe) deficiencies in broad beans on highly calcareous soils in the SE of SA.

Outcomes of this project are focused on the development of management strategies which improve soil condition, crop early vigour, crop productivity and farm profitability.

Results

  • Higher seeding rates and nutrition at sowing is effective at achieving high plant densities, crop biomass and grain yield.
  • CCM in the topsoil improved crop vigour, biomass and grain yield
  • Short-term topsoil strategies resulted in better gains in crop biomass and yield when compared to longer-term subsoil strategies.
  • High soil strength is an issue in calcareous soils but positive responses to deep ripping are not common and are usually limited by the hostile subsoil.
  • Soil amendments had little impact when placed deep during ripping, so amelioration of these soils has little merit.
  • Crops growing on a mildly calcareous soil were less responsive to the strategies investigated than those grown on highly calcareous soils of upper EP.
  • Severe yellowing in broad beans was overcome with multiple applications of an iron chelate (Fe-EDDHA) and resulted in large grain yield increases. Applications of Mn did not improve bean production.

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